Dopant-induced shape evolution of polyhedral magnetite nanocrystals and their morphology/component-dependent high-rate electrochemical performance for lithium-ion batteries

Abstract

Monodisperse Mn x Fe 3Àx O 4 (x ¼ 0, 0.3, 0.6) polyhedrons enclosed by {100}/{111} facets with different area ratios were synthesized through the thermolysis of Fe(acac) 3 and Mn(acac) 2 by effectively tuning the Mn/Fe ratio to mediate the adsorption properties of oleic acid (OA) on crystal surfaces after annealing treatment in N 2 , and studied as high rate ($1 A g À1 ) anode materials for lithium ion batteries (LIBs). The electrochemical results show that Mn 0.6 Fe 2.4 O 4 octahedra possess the best rate cycling performance compared to that of Mn 0.3 Fe 2.7 O 4 cuboctahedra and Fe 3 O 4 cubes, characterised by a 500th discharge capacity of 803.5 mA h g À1 at 1 A g À1 and a rate capability of 661.5 mA h g À1 when cycled at 4 A g À1 , as a result of high electrochemical activity of {111} facets with the highest Fe atom surface density. The present results prove that the substitution of Fe by Mn in the spinel-type anode materials can result in better cycle stability and it would be helpful for the further understanding of Fe 3 O 4 based anode materials and provide a simple and practical route to design high rate anode materials for lithium-ion batteries.

Shape Dependence on the Electrochemistry of Uncoated Magnetite Motifs

“…The resulting octahedra incorporating the highest amount of Mg doping yielded an increased cycling performance as compared with that of the other morphologies produced; these motifs maintained a discharge capacity (after 500 cycles) of 803.5 mA h g −1 at 1 A g −1 coupled with a rate capability of 661.5 mA h g −1 when cycled at 4 A g −1 . 7 Furthermore, another study explored the effects of exposing (111) and (100) facets of magnetite polyhedra for LIB applications, implying the significance of expanding the number of unique and potentially more reactive facets as a means of improving their activity. 8 Therefore, given this literature precedence, within this work, we intend to probe the roles of (i) the nature of exposed facets and (ii) the associated morphology with respect to measured electrochemical performance within the context of acquiring insights into structure-property correlations relevant for battery applications.…”